A. James Clark School of Engineering

Permanent URI for this communityhttp://hdl.handle.net/1903/1654

The collections in this community comprise faculty research works, as well as graduate theses and dissertations.

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Now showing 1 - 10 of 24
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    Model-Based Design and Formal Verification Processes for Automated Waterway System Operations
    (MDPI, 2016-06-07) Petnga, Leonard; Austin, Mark
    Waterway and canal systems are particularly cost effective in the transport of bulk and containerized goods to support global trade. Yet, despite these benefits, they are among the most under-appreciated forms of transportation engineering systems. Looking ahead, the long-term view is not rosy. Failures, delays, incidents and accidents in aging waterway systems are doing little to attract the technical and economic assistance required for modernization and sustainability. In a step toward overcoming these challenges, this paper argues that programs for waterway and canal modernization and sustainability can benefit significantly from system thinking, supported by systems engineering techniques. We propose a multi-level multi-stage methodology for the model-based design, simulation and formal verification of automated waterway system operations. At the front-end of development, semi-formal modeling techniques are employed for the representation of project goals and scenarios, requirements and high-level models of behavior and structure. To assure the accuracy of engineering predictions and the correctness of operations, formal modeling techniques are used for the performance assessment and the formal verification of the correctness of functionality. The essential features of this methodology are highlighted in a case study examination of ship and lock-system behaviors in a two-stage lock system.
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    Compositional Approach to Distributed System Behavior Modeling and Formal Validation of Infrastructure Operations with Finite State Automata: Application to Viewpoint-Driven Verification of Functionality in Waterways
    (MDPI, 2018-01-12) Austin, Mark A.; Johnson, John
    Now that modern infrastructure systems are moving toward an increased use of automation in their day-to-day operations, there is an emerging need for new approaches to the formal analysis and validation of system functionality with respect to correctness of operations. This paper describes a compositional approach to the multi-level behavior modeling and formal validation of large-scale distributed system operations with hierarchies and networks of finite state automata. To avoid the well-known state explosion problem, we develop a new procedure for viewpoint-action-process traceability, thereby allowing parts of a behavior model not relevant to a specific decision to be removed from consideration. Key features of the methodology are illustrated through the development of behavior models and validation procedures for polite conversation between two individuals, and lockset- and system-level concerns for ships traversing a large-scale waterway system.
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    Adsorption Kinetic Model Predicts and Improves Reliability of Electrochemical Serotonin Detection
    (MDPI, 2023-01-09) Chapin, Ashley Augustiny; Han, Jinjing; Ghodssi, Reza
    Serotonin (5-HT) is a neurotransmitter involved in many biophysiological processes in the brain and in the gastrointestinal tract. Electrochemical methods are commonly used to quantify 5-HT, but their reliability may suffer due to the time-dependent nature of adsorption-limited 5-HT detection, as well as electrode fouling over repeated measurements. Mathematical characterization and modeling of adsorption-based electrochemical signal generation would improve reliability of 5-HT measurement. Here, a model was developed to track 5-HT electrode adsorption and resulting current output by combining Langmuir adsorption kinetic equations and adsorption-limited electrochemical equations. 5-HT adsorption binding parameters were experimentally determined at a carbon-nanotube coated Au electrode: KD = 7 × 10−7 M, kon = 130 M−1 s−1, koff = 9.1 × 10−5 s−1. A computational model of 5-HT adsorption was then constructed, which could effectively predict 5-HT fouling over 50 measurements (R2 = 0.9947), as well as predict electrode responses over varying concentrations and measurement times. The model aided in optimizing the measurement of 5-HT secreted from a model enterochromaffin cell line—RIN14B—minimizing measurement time. The presented model simplified and improved the characterization of 5-HT detection at the selected electrode. This could be applied to many other adsorption-limited electrochemical analytes and electrode types, contributing to the improvement of application-specific modeling and optimization processes.
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    Characterization and Modeling of Brushless DC Motors and Electronic Speed Controllers with a Dynamometer
    (2019) Brown, Robert; Chopra, Inderjit; Aerospace Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    The global drone market is expected to grow from $4.9 billion to $14.3 billion within the next decade, indicating a heavy demand for high performance electric aircraft. Modern drones are propelled with brushless DC (BLDC) motors and electronic speed controllers (ESCs). However, a current lack of information concerning the performance and efficiency of BLDC motors and ESCs prevents their use in rigorous aircraft design. Low cost hobby ESCs and BLDCs are typically used in research aircraft, but few technical details are released by their manufacturers. To better understand these devices, a custom dynamometer was constructed to study the performance of ESCs and BLDC motors. By properly recording the DC, AC, and mechanical power, information on peak efficiency and performance for the ESCs and BLDC motors are determined experimentally. Motors between 920 KV to 2500 KV were tested with 18 A, 30 A, and 40 A ESCs. A combination of these tests were carried out at 7.2 V, 11.1 V, and 14.8 V DC to explore trade offs in the design process. While typically neglected in formal analysis, this work seeks to better understand the power loss mechanisms in ESCs, as it was found that ESCs could have efficiencies as low as 65%, reducing the overall efficiency of the system considerably. This custom dynamometer features a load varying device, power analyzers, and a unique two DAQ setup to properly capture the high frequency electrical signals of BLDC motors. From the sets of experimentally recorded motor and ESC tests, a novel analytical model is developed to predict the performance of ESCs and BLDC motors. At the heart of this modeling effort is describing the 3 phase AC circuit as a single equivalent circuit, which encapsulating the motor’s performance. This work is critical in the design process, as properly sizing ESCs, motors, and rotors for an electric aircraft can improve aircraft endurance and range. Performance metrics are extracted from experimental results and are fit into the analytical model. Predictions for the system’s mechanical power, AC power, and DC power agree well with experimental results, demonstrating applicability of the robust model.
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    Phonon Modeling in Nano- and Micro- scale Crystalline Systems
    (2018) VanGessel, Francis; Chung, Peter; Mechanical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    Submicrometer phonon systems are becoming increasingly relevant in modern day technology. Phonon mechanisms are notably relevant in a number of solid-state devices including lasers, LEDs, transistors, and thermoelectrics. Proliferation of these devices has been driven by advancements in silicon-on-insulator technology. These advancements have allowed for the manufacture of devices with complex nanostructures and dimensions deep in the sub-microscale regime. However, accompanying improvements in the manufacture and design of novel crystalline systems is the requirement for accurate computational approaches for phonon modeling in nanostructured, anisotropic, and complex materials. The phonon Boltzmann transport equation is uniquely well suited to modeling energy transfer at the nano- and micro- meter length scales and is therefore an excellent candidate for this simulation task. However, current Boltzmann modeling approaches utilize a range of assumptions and simplifications that restrict their validity to isotropic, nominally one or two dimensional, or compositionally simple systems. In this dissertation we present an original finite volume-based methodology for the solution of the three dimensional full Brillouin zone phonon Boltzmann transport equation. This methodology allows for separate real and reciprocal space discretization. By taking a sampling of vibrational modes throughout the first Brillouin zone our methodology captures three unique sources of phonon anisotropy. We investigate the effect of phonon anisotropy in a fin field effect transistor, calculating the effect that incorporating various sources of anisotropy has on the resultant temperature fields. In a second study, we consider phonon flow through silicon nanowires with a modified boundary geometry. The three-dimensional flow fields are calculated and thermal transport below the Casimir limit is observed. Reduction in thermal conductivity is a result of maximizing the phonon backscatter that occurs in our phononic system. The backscatter serves to create regions of highly misaligned phonon flux. In addition, our silicon nanowire geometry has properties analogous with a high-pass phonon filter. In the final study we apply our Boltzmann transport methodology to the simulation of phonon transport in the energetic material, RDX. We study phonon transport in the vicinity of a material hotspot, the location at which chemistry initiates in the material. By applying Boltzmann modeling, applied for the first time to this material, we gain valuable insights into the interplay between thermal transport and phonon modes linked with initiation.
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    Data-Driven Wildfire Propagation Modeling with FARSITE-EnKF
    (2016) Theodori, Maria Faye; Trouve, Arnaud; Fire Protection Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    The goal of this study is to provide a framework for future researchers to understand and use the FARSITE wildfire-forecasting model with data assimilation. Current wildfire models lack the ability to provide accurate prediction of fire front position faster than real-time. When FARSITE is coupled with a recursive ensemble filter, the data assimilation forecast method improves. The scope includes an explanation of the standalone FARSITE application, technical details on FARSITE integration with a parallel program coupler called OpenPALM, and a model demonstration of the FARSITE-Ensemble Kalman Filter software using the FireFlux I experiment by Craig Clements. The results show that the fire front forecast is improved with the proposed data-driven methodology than with the standalone FARSITE model.
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    MODELING AND EXPERIMENTAL ANALYSIS OF PHASED ARRAY SYNTHETIC JET CROSS-FLOW INTERACTIONS
    (2014) HASNAIN, ZOHAIB; Flatau, Alison B; Aerospace Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    Synthetic Jet Actuators (SJAs) are fluidic devices capable of adding momentum to static or non-static bodies of fluid without adding mass. They are therefore categorized as zero-net-mass-flux (ZNMF) momentum source. In its simplest compact form a SJA consists of an oscillatory surface connected to a cavity with a single exit orifice through which the fluid enters and exits. SJA technology has been utilized in applications ranging from boundary layer control over aerodynamic surfaces to fluidic mixing in dispersion applications. The ZNMF nature of the technology means it is not subject to constraints experienced by traditional momentum sources that require the addition of mass in order to impart momentum. The momentum that can be added by a single SJA is limited by the energy transfer capabilities of the oscillating surface. In modern SJAs this surface usually is a piezoceramic/metal composite subjected to a high voltage AC signal. For applications such as flow control over aerodynamic surfaces, modern SJAs are used in an array configuration and are capable of altering the flow momentum by values ranging from 0.01-10%. While it is possible to build larger actuators to increase this value the benefits associated with the compact size would be lost. It is therefore desirable to tune other parameters associated with SJA arrays to increase this value. The specific motivation for this study comes from the desire to control the momentum addition capacity of a specific SJA array, without having to alter any geometric parameters. In a broader sense this study focuses on understanding the physics of SJA interaction in array configuration through experiments which are then used to guide in the design of modeling technique that predicts SJA array behavior in cross-flows. The first half of the project focused on understanding SJA behavior through modeling. Numerical techniques were initially used to model SJA and SJA arrays in cross-flows. Reduced numerical models were then developed from the full momentum equations. Analytical methods to solve these reduced order models were then implemented in order to cut down on solution time. A wave equation based solution to the stream and vorticity formulation of the momentum equations was implemented to predict SJA behavior. For the experimental component of the project, a finite span high aspect ratio orifice SJA was designed and characterized through Constant Temperature Anemometry (CTA). Two of these SJA were then placed in close proximity to one another. The relative phase of operation between the two jets was altered and the resulting flow field was measured through Particle Image Velocimetry (PIV). This process was repeated for different sets of array spacing, and SJA to cross-flow velocity ratio. For specific choices of these parameters a 40% increase in momentum addition was observed. The experimental results were used to validate the modeling techniques. In general reasonable agreement between the modeling and experiment was observed in specific domains of the flow field.
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    Detailed Measurements of Fire-Induced Mixing Phenomena
    (2014) Layton, Thomas George; Marshall, Andre W; Fire Protection Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    This study successfully validated the use of salt-water analog modeling as an effective diagnostic tool for predicting fire-induced flows. A technique was developed for taking measurements using combined Planar Laser-Induced Fluorescence (PLIF) and Particle Image Velocimetry (PIV), and results were analyzed with respect to smoke filling as well as transient ceiling layer dynamics, and turbulent mixing intensity. Data was shown to be in good agreement with theory, further validating the salt-water analogy as a tool for diagnostics, prediction, and scaling of fire phenomena.
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    Development of a Model for Flaming Combustion of Double-Wall Corrugated Cardboard
    (2012) McKinnon, Mark; Stoliarov, Stanislav I; Fire Protection Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    Corrugated cardboard is used extensively in a storage capacity in warehouses and frequently acts as the primary fuel for accidental fires that begin in storage facilities. A one-dimensional numerical pyrolysis model for double-wall corrugated cardboard was developed using the Thermakin modeling environment to describe the burning rate of corrugated cardboard. The model parameters corresponding to the thermal properties of the corrugated cardboard layers were determined through analysis of data collected in cone calorimeter tests conducted with incident heat fluxes in the range 20-80 kW/m2. An apparent pyrolysis reaction mechanism and thermodynamic properties for the material were obtained using thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC). The fully-parameterized bench-scale model predicted burning rate profiles that were in agreement with the experimental data for the entire range of incident heat fluxes, with more consistent predictions at higher heat fluxes.
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    Control-Oriented Reduced Order Modeling of Dipteran Flapping Flight
    (2011) Faruque, Imraan A.; Humbert, J Sean; Aerospace Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    Flying insects achieve flight stabilization and control in a manner that requires only small, specialized neural structures to perform the essential components of sensing and feedback, achieving unparalleled levels of robust aerobatic flight on limited computational resources. An engineering mechanism to replicate these control strategies could provide a dramatic increase in the mobility of small scale aerial robotics, but a formal investigation has not yet yielded tools that both quantitatively and intuitively explain flapping wing flight as an "input-output" relationship. This work uses experimental and simulated measurements of insect flight to create reduced order flight dynamics models. The framework presented here creates models that are relevant for the study of control properties. The work begins with automated measurement of insect wing motions in free flight, which are then used to calculate flight forces via an empirically-derived aerodynamics model. When paired with rigid body dynamics and experimentally measured state feedback, both the bare airframe and closed loop systems may be analyzed using frequency domain system identification. Flight dynamics models describing maneuvering about hover and cruise conditions are presented for example fruit flies (Drosophila melanogaster) and blowflies (Calliphorids). The results show that biologically measured feedback paths are appropriate for flight stabilization and sexual dimorphism is only a minor factor in flight dynamics. A method of ranking kinematic control inputs to maximize maneuverability is also presented, showing that the volume of reachable configurations in state space can be dramatically increased due to appropriate choice of kinematic inputs.